Today, carbon dioxide emissions from automobiles are required to be reduced. Since reduction of weight of vehicles greatly influences improvement of fuel efficiency, the weight of wire harnesses for connecting electrical components are also required to be reduced. Therefore, it has been studied to, for example, replace copper-based materials which are conventionally used for electric wires or the like used for the wire harnesses with an aluminum material and such an aluminum material has been used for some electric wires.
A terminal usable for connecting electric wires to each other or for connecting an electric wire to an assisting part or component is usually formed of a nobler metal material than aluminum.
However, a connection structural body, obtained by stripping a tip of an insulated wire of a conductor cover to expose a tip of an aluminum conductor and pressure-bonding the tip of the aluminum conductor to the above-mentioned terminal, has a problem that the aluminum conductor formed of an aluminum material less noble than the metal material used to form the terminal is corroded as a result of contact of the aluminum conductor and the terminal; namely, has a problem of galvanic corrosion.
The above-mentioned galvanic corrosion is a phenomenon that when water as an electrolytic solution is attached to a site at which a nobler metal material and a less noble metal material contact each other, a corrosion current is generated, and as a result, the less noble metal material is, for example, corroded, dissolved, or extinguished. In the case of a connection structural body mentioned above, the following problem occurs. The aluminum conductor of the insulated wire is pressure-bonded to a pressure-bonding section of the terminal formed of a nobler metal material than aluminum, and as a result, the aluminum conductor is corroded, dissolved, or extinguished. Therefore, the electric resistance is raised. This causes a problem that the connection structural body cannot exhibit a sufficient conducting function.
In order to prevent galvanic corrosion of such an aluminum conductor used in a connection structural body in which different types of metal materials, namely, a terminal formed of a nobler metal material than aluminum and the aluminum conductor of the insulated wire are connected to each other, Patent Documents 1 and 2, for example, propose the following technology on a crimp terminal. A main body of the crimp terminal is formed of an aluminum material, and an elastic piece for supporting a contact of a terminal, which is to be electrically connected to the crimp terminal, is formed of an iron-based material.
It is described in the above-identified publications that since the wire conductor and a substrate of the main body of the terminal are both formed of an aluminum material and thus have an equal potential, even when the aluminum conductor is connected to the main body of the terminal, the aluminum conductor is prevented from being corroded.
However, the crimp terminal proposed in each of Patent Documents 1 and 2 has a structure in which the elastic piece is assembled to the main body of the terminal formed of a different metal material from that of the elastic piece. Thus, the problem of galvanic corrosion occurs between the main body of the terminal and the elastic piece.
This will be described in more detail. The aluminum material used to form the main body of the terminal is less noble than the iron-based material used to form the elastic piece. Therefore, when an electrolytic solution such as water or the like is attached, the main body of the terminal itself is corroded. This causes pitting corrosion or the like, and as a result, the elasticity of the elastic piece, and the mechanical strength and the like of the terminal itself cannot be maintained. In addition, the conductor is corroded in the pressure-bonging section, which increases the electric resistance, and as a result, the conductor may undesirably lose functions thereof.
In addition, the technology proposed in Patent Documents 1 and 2 is difficult to be applied to the conventional processing procedure for producing a terminal, namely, a continuous procedure of punching out the substrate of the terminal with a press and bending the substrate. Thus, it is difficult to mass-produce the terminal with the technology proposed in Patent Documents 1 and 2.
Meanwhile, in the case where the crimp terminal is entirely formed of an aluminum material, the crimp terminal is usually treated as follows for the purpose of providing a good electric connection with a component to which the crimp terminal is to be connected or pressure-bonded. For example, at least a surface of a connection section or a pressure-bonding section of the crimp terminal is covered with a conductive contact body having high electric connectability and containing a nobler metal material than the aluminum material, for example, is plated with, for example, tin, gold, a copper alloy or the like.
However, when an electrolytic solution is attached to a contact part where the crimp terminal formed of an aluminum substrate and the conductive contact body containing a nobler metal material than the aluminum material, there occurs a problem that galvanic corrosion occurs to the contact part of the crimp terminal formed of the aluminum substrate, which undesirably decreases the conductivity with the other conductive members.
In addition, in the case where a terminal to which the connection section is to be connected is an aluminum terminal, or in the case where a wire conductor to which the pressure-bonding section is to be pressure-bonded is an aluminum terminal, there occurs a problem that the above-mentioned conductive contact body used to cover at least the surface of the connection section or the pressure-bonding section of the crimp terminal causes galvanic corrosion of the aluminum wire conductor and the aluminum terminal.